Method and means for modulating a magnetron beam tube



Aug. 20, 1963 E. D. AYERS 3,101,429

METHOD AND MEANS FOR MODULATING A MAGNETRON BEAM TUBE Original Filed Feb. 24, 1954 2 Sheets-Sheetl INVENTOR 1963 E. D. AYERS 3,101,429

METHOD AND MEANS FOR MODULATING A MAGNETRON BEAM TUBE 2 Sheets-Sheet. 2

Original Filed Feb. 24, 1954 Flg. 5

a 25 g L 0 7 1,

I/ 82 78 Hp 8 28A 26A [5 22 88; 74 84 78 l INVENTOR III-Ill United States Patent 25 Claims. (Cl. 315-30) This invention relates to magnetron type beam tubes and particularly to means for and a method to modulating the electron stream of such tubes. This application is a continuation of application Serial No. 412,229, now abandoned, filed February 24, 1954.

Magnetron type multiple position beam tubes make use of crossed electrostatic and magnetic fields in their operation. Usually the magnetic field is provided by a hollow cylindrical permanent magnet which encompasses the tube and whose flux permeates the tube in lines which are substantially parallel to an elongated cathode electrode which is centrally disposed within the tube. Magnetron type beam switching tubes, which are an example of this general type, usually have at least two arrays of electrodes surrounding the elongated thermionic cathode. A hollow cylindrical array of symmetrically disposed beam forming and directing electrodes, commonly known as spade electrodes, surrounds the cathode and is concentric with respect to it.

Each spade electrode is insulated from the other spade electrodes and is usually connected to a source of potential which is positive with respect to the cathode through a spade impedance such as a resistor. The spade electrodes are usually coextensive in length with the electron emissive portion of the cathode and have a curved, usualy U-shaped, transverse cross-sectional configuration. The open part of the spade faces outwardly with respect to the cathode.

An array of symmetrically disposed electron receiving or target electrodes which has a larger diameter than the array of spade electrodes surrounds the spades and usually constitutes the outer array of electrodes of the tube. The target electrodes are normally equal in number to the spade electrodes, and each target is aligned with the space between two adjacent spades whereby electrons passing through the space impinge on the target electrode which is associated therewith. Like the spades, each target electrode is usually connected to a source of potential which is positive with respect to the cathode through an individual impedance member, usually a resistor. The output signal to be taken from each target electrode is developed across its target impedance member. These electrode arrays are associated in groups which define the multiplicity of beam positions within the tube. Each spade and an associated target define a beam-receiving electrode group for a beam position.

Other types of multiple position beam switching tubes may have additional types of electrodes which serve special functions. For instance, in one such type, a slotted sleeve-like hollow cylindrical anode electrode is disposed between the spades and the target electrode. The slots in the anode extend longitudinally thereof and are disposed in alignment with and opposite to the spaces between the various spades. This anode serves, among other things, as an electrostatic shield between the target and the spade electrodes in order that large voltage swings on the targets do not afiiect the beam switching and holding stability of the tube. Also, the anode slots may be of varying sizes and configurations and thus provide a coded output. In still another type of tube, an array of rod-like switching electrodes is positioned between the targets and the spades, there being one of 3, l h l A29 Patented Aug. 20, 1963 the rod-like switching electrodes disposed between an edge of each spade and the target electrode which is associated with the next adjacent spade. These electrodes provide a convenient means for switching the electron beam from one beam position to another by means of negative pulses having an amplitude of only a few volts.

All of the above-mentioned magnetron beam tube types, and other similar types of tubes, operate substantially as follows: When all of the spades are at the potential of the spade power supply, the relationship between the electrostatic and magnetic fields within the tube and particularly in the cathode-spade is such that electrons emitted from the cathode tend to follow curved paths around the cathode and substantially no electrons impinge on the spades or other outer electrodes of the tube. If, however, the potential on one of the spades is lowered to, or near to, the potential of the cathode, the configuration of the electrostatic field is changed, especially in the vicinity of the spade having the lowered potential, and, if the change is of sufiicient magnitude, a stream or beam of electrons is formed between the cathode and the leading edge of that spade. The edge of the spade to which the beam is attracted is determined by the direction of rotation of the electron beam within the tube (which in turn is determined by the polarity of the magnetic field which permeates the tube). The electron beam locks in on the edge of the spade which is furthest in the direction of the rotation of the electron beam, and this edge is commonly called the leading edge.

The electrons impinging on the spade cause electron flow through the spade impedance and, if the spade resistor value is properly chosen, the electron flow through it reduces the potential of the spade sufficiently to maintain the electron beam locked in on the spade even though the external means for reducing the potential of the spade be removed.

Usually the electron beam (or stream) is advanced from one beam position or spade to another in the tube by some means which causes the electron beam to fan out, widen or otherwise change its shape so that portions of the beam impinge both on the spade upon which the beam is locked in and upon the spade which is adjacent thereto in the direction of rotation of the beam. When the electron beam or stream impinges on the next adjacent spade, a voltage drop occurs across the spade impedance of that spade, causing still more electrons in the beam to be attracted thereto, further dropping the potential of the spade. When the spade potential drops below a critical value, or stated otherwise, when the electrostatic field alteration exceeds a critical value, the electron beam, due to the rotational influence of the magnetic field, will advance to the next spade or beam position. The particular means utilized for causing the electron beam to fan or spread out in order to switch from one beam position to another will be described in detail in connection with later-described embodiments of the present invention.

Magnetron type beam tubes have found considerable use as counters, for example, in pulse code modulation systems and in other control or switching devices.

When magnetron type switching tubes are utilized in communications equipment, and in some types of control equipment, it is often desirable to modulate or change the density of the electron stream of the tube. In the past, the modulation of such tubes has been accomplished usually by applying the modulating signal to the cathode circuit of the magnetron type beam switching tube. Alternatively, in some magnetron type beam switching tubes of special construction, a control grid surrounds the centrally disposed cathode. The modulation signal may be applied to this grid and in this manner, control the density of the electron beam.

With each of these modulation systems, normally only a single modulation signal may be used to modulate the output at each beam position of the switching tube. Further, if grid modulation is used, the grid wires may adversely affect the beam formation within the tube. On the other hand, the changing of the cathode-spade potential which occurs when cathode modulation is used, may adversely afiect the operation of the tube. For example, if the spade-cathode potential is varied beyond a maximum or minimum value which in some tubes may be quite critical the beam will be extinguished, or under less severe variations of the spade-cathode voltage, the switching grid voltage required to cause the beam to advance from beam position to beam position will vary.

In many applications, it would be desirable to impress a different modulation signal on the beam at each beam position. With such an arrangement, a very high speed time division multiplex system would result if the outputs of all the beam positions were connected in parallel. Other tubes have been devised in which separate modulation signals could be introduced at each beam position, but these tubes are rather complex, expensive, are not magnetrons, and are not capable of switching speeds which compare favorably with those attainable with magnetron type beam switching tubes. Most of the tubes which permit the output of each beam position to be modulated by a separate signal utilize grid modulation, a separate grid structure being disposed adjacent to each output electrode. Consequently, in order to provide a significant percentage of modulation cf the output signal, the amplitude of the modulating signal is usually large as compared with the signal amplitude required to produce similar modulation when the grid is disposed closer to the cathode. Further, these tubes are not beam tubes, and thus require a larger cathode than do beam tubes tor a given power output. Since electrons emanate from the cathode in all directions in such tubes, a separate series of grids, each disposed between the cathode and an anode, is provided, and these grids may be selectively biased to cut, oil? electron flow to all but a selected output electrode or electrodes. Thus, these tubes comprise a cathode, twenty grids and ten targets or anodes for a ten position tube. This results in a very complex tube structure, and yet additional means, external to the tube, must be provided for selectively cutting on or oil electron flow to chosen targets.

Ifthe tubes are power tubes, considerable power must be'absorbed by the grids, and this often results in heat dissipation problems within the tube. Further, the energy absorbed in the grid structure is wasted so tar as useful output is concerned.

'Fubes of the magnetron switching type may be used-as power tubes or as voltage amplifier tubes as well as for the electronic commutator, counter and other uses for which they are better known. For such uses, the coaxial commutator" type tube may be more complex in structure than is required. The complexity may result in larger interelectrode capacitances than desired and, of course, in larger cost.

An object of this invention is to provide an improved method of and means [for modulating a magnetron type beam tube.

Another object of this invention is to provide an improved magnetron type beam tube of simplified construction.

A turther object of the present invention is to provide an improved modulation system for use with multiple position beam tubes in which the electron beam may be modulated by a separate signal in each beam position.

Still another object of this invention is to provide an improved method of modulating a magnetron type beam tube in which the position of the electron beam within the tube determines which of a plurality of constantly applied modulation signals will modulate the electron beam.

An additional object of the present invention is to provide a magnetron beam tube which provides positive or negative output signals, or both.

Broadly speaking, modulation of the electron beam or stream in a magnetron type beam tube is accomplished by applying a varying potential of a few volts amplitude to an electrode which is disposed adjacent to the electrode which per-terms the beam holding functions, but out of the path of the electron beam or stream. The electrode to which the modulating signal is applied is adjacent to the lagging side of the electron beam.

A simplified magnetron beam tube in accordance with this invention and having only a single nor-ma 7 output position and a beam position for initially causing an electron beam to be formed is provided.

The invention, as well as additional objects and advantages thereof, will be best understood trom the following description when read in connection with the accompanying drawings, in which:

FIG. 1 is an isometric view of a magnetron type multiple position beam switching tube which is suitable for use with the present invention;

FIG. 2 is a sectional view taken along the lines 2-2 of FIG. 1;

FIG. 3 is an isometric view of a simplified magnetron type beam tube in accordance with the present invention;

FIG. 4 is a sectional view taken i ong the line 44 of FIG. 3;

FIG. 5 is a schematic diagrammatic view of a modulation system in accordance with the present invention;

FIG. 6 is a simplified schematic view of an embodiment of the present invention in which a modulating signal is applied simultaneously to all spades and in which diode feedback is utilized to control the potential on the preceding spades;

FIG. 7 is a simplified adaptation of the embodiment of the invention shown in FIG. 5; and

FIG. 8 is a simplified schematic view of an embodiment cf the present invention in which internal feedback is utilized to control the potential level of the preceding spade to which the modulating signal is applied.

Referring to FIGS. 1 and 2, there is shown a multiple position beam switching tube 20. A cathode 22, illustrated as being of the oxide-coated indirectly heated type, is centrally disposed within the evacuated envelope 24. A circular array of elongated beam tonming and directing or spade electrons 26 surrounds the cathode 24.

'There are ten of the trough-shaped spade electrodes 26, one for each beam position, and each spade electrode is insulated from the others. The outermost array in the tube comprises ten electron receiving elongated target electrodes 28 each having a generally L-shaped crosssectional configuration. The base 29 ot the L portion or each target 28 is interleaved between the outwardly extending parts of one of the spade electrodes 26.

A circular array of rod-like switching grid electrodes 30 is disposed generally between the spade array and the target array. Each of the switching grids 30 is generally in alignment with an extension of a side of a spade electrode 26.

In the tube shown in FIGS. 1 and 2, there are ten beam positions. A beam position includes a spade 26, a target 28, and a switching grid 30. The electron stream or beam locks in on a spade 26 with the larger portion of the beam impinging on the target electrode 28 associated with that spade. The target electrode associated with a spade, in the tube illustrated in FIGS. 1 and 2, for example, is the tanget which is interleaved with that spade, assuming the electron beam to be rotating in a clockwise direction. The switching grid of the beam position is the one which is utilized to cause the beam to switch from the spade on which it is locked in to the next adjacent spade.

The tube 2% is surrounded by an external magnet 32 which has flux lines extending through the tube and providing a substantially uniform axial field between the cathode 22 and the various arrays of electrodes. The flux, as indicated by the symbol 23, is of a polarity which tends to advance the electron beam in a clockwise direction. It is particularly desirable that the magnetic field be uniform in the cathode-spade area. The magnetic field may be provided by a permanent magnet, as shown, or by an electromagnet or combination of the two types.

The tube 34 shown in FIGS. 3 and 4 is a modification of the magnetron type beam switching tube of FIGS. 1 I

and 2. The tube 34 has a centrally disposed thermionic cathode 36 and two spade electrodes 38, 41 which are disposed with respect to the cathode 36 in the same manner as two adjoining spades 26 of the tube 20 are disposed with respect to its cathode 22. The space which is defined by the remaining spades 26 in the tube 20 is replaced by a single electrode 42 which is of sheet material which is bent so that its inner surface is substantially equidistant from the cathode 36 at all points. The exact part of a circle which the edge of the electrode 42 forms depends on the relative size and spacing of the spades 3S and 4-3. The tube 34 has two target electrodes 44, 46 associated with the spades 38, 46, respectively. The targets 44, 46 are illustrated as being of the same general configuration as the targets 28 of the ten position tube 20*, although other electrode configurations such as flat sheet-like targets or targets presenting curved surfaces to the electron stream could be utilized. These two beam receiving positions define two beam paths, one to target 44 and one to target 46. A screen grid 48 is disposed adjacent to the surface of the target 46 which faces the cathode 36. The function of this electrode will be discussed later.

The operation of the tube 34 may be as follows, by way of example: The cathode 35 is at ground potential, the electrode 42 is directly connected to a source of positive potential and the spade 40', screen grid 48, and target 46 are each connected to a source of positive potential through a separate load impedance. The target electrode 44 is connected to the spade 4t and the spade impedance 56 serves as the load impedance to both electrodes. The screen grid impedance 52 and the target impedance 54 for the target 46 are each shown connected to the same source of positive potential 56, although these electrodes, as well as the spade electrode 40 may, if desired, be maintained at different operation potentials.

The spade 38 is connected to a negative biasing source 58 through a resistor 60. Whether or not the spade 38 need be biased at a negative potential or merely grounded depends on the electrode configuration and desired operation of the tube. Modulation signals may be applied (to the terminal '62) across the resistor 60. The polarity of the magnetic field surrounding the tube, as previously mentioned, is such that the electron beam tends to rotate in a clockwise direction. When operating potentials are applied to the tube 3-4, an electron beam 64 is formed and attempts to lock in a path terminating in part on the spade 38. However, when the beam follows this path, a large part of the electron beam 64 impinges on the target 44, causing a potential drop across the spade resistor Sit, and lowering the potential of the spade 40 to, or near to, the potential of the cathode 36, thereby causing the electron beam 64 to rapidly transfer to a second beam path and lock in on the spade 4d. The output signal from the tube 34 is normally taken across the target resistor 54 from the terminal 66.

The screen grid 4-8 is utilized to provide a better pentode output characteristic of the tube. The surface of the target 46 which faces the screen grid 48 may, if desired, have a secondary emissive coating (or the target 46 itself may be of a material which has good secondary emission capabilities), in which case the screen grid 48 would serve as a collector of secondary electrons emitted from the target. This arrangement would provide a positive rather than a negative output signal from the target 46. A negative output-signal could simultaneously be obtained across the screen grid resistor 52. The use of a similar secondary emissive target in a ten count tube, in the zero position, for example, would provide a simple means of obtaininga positive output pulse which could be applied (by capacity coupling, for example) to another tube which is connected in cascade with the first tube or utilized for other driving purposes. In such multiple count tubes, the screen grid secondary electron collector corresponding to the screen grid 48 would of necessity have to shield the advance (or one spade in this case) from the secondary electrons emitted from the zero target, otherwise the beam might shift due to the potential drop thus caused across the spade impedance of the advanced spade. The same arrangement could be applied, if desired, to all beam positions of the tube, but would result in a somewhat complex electrode structure.

In accordance with the modulation system aspects of the present invention, it has been found that lowering the potential of the spade which precedes the one on which the beam is locked in causes the electron beam current to increase. This effect increases as the potential on the preceding spade approaches cathode potential and is eflFective even at spade potentials which are below cathode potential. Thus, in accordance with the present invention, as applied to FIGS. 3 and 4, a modulating signal having a relatively small amplitude, when applied to the terminal 62, causes the electron beam to be modulated in accordance with the amplitude of the applied modulating signal. The fact that the electrode 42 is connected directly to a source or" positive potential prevents the electron beam 64 from advancing beyond the spade 40, since the electrode 42 cannot undergo the change of potential which would i be required to cause the electron beam 64 to switch. 'It should be noted that the modulating electrode is not in the electron path and consequently absorbs no power from the electron beam as does a conventional grid structure which is disposed in the electron stream. While tubes of the magnetron switching type are usually thought of as counter type tubes, they may also be constructed and utilized as power devices. Other advantages of the modulation system in accordance with the present invention will be discussed in connection with FIGS. 5-8, inclusive.

Referring to FIG. 5, there is shown an embodiment of the present invention in which means are provided for impressing a separate modulating signal on the electron beam at each beam position of a ten position tube of the variety illustrated in F168. 1 and 2. FIG. 7 illustrates, in simplified form, the feedback and modulation input arrangement of one of the beam positions of FIG. 5. Because the circuit details for each of the ten beam positions are similar, the detailed description of a single beam position and the modulation of the electron beam at only one position will be given. The polarity of the magnetic field which provided in conjunction with the tube is such that the electron beam will tend to rotate in a clockwise direction around the cathode.

The cathode 22 of the tube is grounded. Each spade 26A is connected to a source of positive potential 70, through a spade resistor 66 and the common lead 68. Each target 28A is connected to a source of positive potential 72 through a target impedance member 74 and the common lead 76. The output signal at each beam position is taken from a terminal 78 connected between target 28A and its impedance members. A feedback arrange ment including an electron tube 80 is provided between the target 28A at each beam position and the spade 26A of the preceding beam position. A resistance member 32 is connected between each target electrode 28A and the cathode 84 of the electron tube 80. A resistance member 86 is also connected between the cathode 84 of the tube 80 and a source of negative potential 88 through the common lead 90. Thus, resistors 74, 82 and 86 are connected in series between a positive and a negative potential and in a sense may all be considered to be part of the target impedance. The values of resistors 74, 82 and 86 are chosen to maintain the target at a desired positive potential, maintain the cathode 84- of the tube 80 at a potential which, in combination with the potential from the bias source 92 which is applied to the tube 86, cuts oil electron flow through the tube 80 under static conditions. However, whenthe electron beam locks in at a beam position, the electrons striking the target cause a voltage drop across the resistor combination (74, 82 and 86), providing an output signal at the terminal 78 and also reduces the bias on the tube 80, making the tube conductive. When the tube is conductive, the potential on spade 26A in FIG. 7 preceding the beam position where the beam is locked in is dropped to near the cathode potential. Since the lowering of the potential of the preceding spade causes the beam current to increase but does not cut off the beam current, the values of resistors '74, 32 and 86 are such that the normal beam current (at the time the beamstrikes the target and before the preceding spade potential is affected) is suiiicient to bias the tube 8%) to a fully conductive state, thereby holding the reference potential of the preceding spade at a constant value, due to the voltage drop across the spade load resistor 66. -A modulation potential source, indicated by the box 94, has its output coupled to the spade 26A of each beam position and varies the spade potential in accordance with the output thereof. Each modulation source, however, is utilized to modulate the electron beam in the next advanced beam position rather than at its own beam position. Ihis is more clearly seen in the simplified view, FIG. 7.

A common modulation source may be used to apply a modulating signal to all of the spades simultaneously, or

a separate modulating signal may be applied to each spade.

Since small variations in spade potential have little 011 no effect On the electron beam current density except when the spade potential is at or somewhere near to the magnetron switching tube), the be applied (constantly) to all affecting the formation or When the electron beam cathode potential (of the modulating signals may the spades Without adversely switching of the electron beam. or stream locks in at a beam position, the feedback arrangement drops the potential on the preceding spade to, or near to, the cathode potential, establishing the condition whereby the beam density will be varied in accordance with the amplitude of the modulating signal. In this manner, a plurality of modulated input signals may, if desired, be time division multiplexed onto a single output signal if all the'target outputs are connected in common. Each target can, of course, be utilized to provide a separate output signal.

In the embodiment of the invention which is shown in FIG. 6, a diode 96 is utilized to reduce the potential of the preceding spade 26B at each beam position. Also, this embodiment of the invention illustrates the application of a modulation signal (via the transformer 98, for

example) between the spade potential source 7 and each spade resistor 66. Thus, the electron beam 64 is modulated by the same signal at each beam position, but without the use of a separate gr d or other modulation electrode.

FIGURE 8 illustrates, in simplified form, the application of the modulation system of the present invention to a beam switching tube having an internal feedback electrode 100 associated with each beam position. Each feedback electrode 100 is disposed in the electron beam path at its beam position and is conductively connected, either inside or outside the tube envelope, to the spade of the preceding beam position. While the modulation signal is illustrated as being applied across the spade load resistor of the preceding spade, the method of applying the modulation illustrated in FIG. 6 would likewise be applicable.

While the met 0d of modulation of the present invention cannot produce 100% modulation of the electron beam, variations in beam density of, for example, 2.5 to l have been achieved in practice, and such variations are adequate for many purposes. Also, the modulation signal or signals may be applied constantly, since the few volts of modulating signal amplitude has little or no e'fiect on the operation characteristics of the tube except at the beam position where the electron beam is locked in.

Further, the modulation system of the present invention may be utilized in signal mixing apparatus where the beam is modulated either by cathode or conventional grid modulation means and simultaneously by the modulation means of the present'invention. While the invention has been illustrated in connection with only a few varieties of magnetron type beam switching tubes, it should be realized that the invention may be applied with equal facility to still other varieties of magnetron beam tube-s. Y

What is claimed is:

1. A modulation system for a magnetron type multiple position beam switching tube having an electron emitting cathode and a plurality of beam receiving electrode groups each including an output electrode and a beam-forming and beam-directing spade electrode and comprising a beam position of the tube, the spade electrode and output electrode of each beam position having a separate load impedance including a resistive member,'and in which the direction the beam tends to advance in the tube is influenced by the polarity of the magnetic field which permeates the tube, said system comprising means including a feedback circuit between the output electrode of each beam position and the adjacent spade electrode which is on the side of said beam position which is opposite the direction in which the magnetic field tends to influence the beam advancement for reducing the potential of said spade to approximately cathode potential, and signal means coupled to said spade for coupling modulation energy to said spade across its load impedance.

2. A modulation system in accordance with claim 1, wherein said means for coupling modulation energy com prises a separate modulation signal source for modulating the beam at each beam position.

3. A modulation system for a magnetron type multiple position beam switching tube having an electron emitting cathode and a plurality of beam receiving electrode groups each including at least one output electrode and a beamforming and beam-directing spade electrode and defining a beam position of the tube, the spade electrode and at least one output electrode of each beam position having a separate load impedance including a resistive member, and in which the direction the beam tends to advance in the tube is influenced by the polarity of the magnetic field which permeates the tube, said system comprising means including a feedback circuit adapted to pass an electrical current unidirectionally between at least one output electrode of each beam position and the adjacent spade electrode which is one the side of said beam position which is opposite field tends to influence the beam advancement for reducing the potential of said last-mentioned spade to approximately oathode potential, signal means coupled to said spade for coupling modulation energy to said spade across its load impedance.

4. A modulation system in accordance with claim 3, wherein the feedback circuit comprises diode coupling between an output electrode of each beam position and the above-mentioned adjacent spade electrode.

5. A modulation in accordance with claim 3, wherein the target impedance of each beam position comprises a resistance network and the said unidirectional feedback circuit includes an electron tube whose bias is controlled by the potential drop across said resistance network and Whose output current flows through the load impedance of said last-mentioned spade.

6. A modulationsystem for a magnetron type multiple position beam switching tube having an electron emitting cathode and a plurality of beam-receiving electrode groups each including at least one output electrode and a beamforming and beam-directing spade electrode and compristhe direction in which the magnetic ing a beam position of the tube, the spade electrode and at least one output electrode of each beam position having a separate load impedance including a resistive member, and in which the direction the beam tends to advance in the tube is influenced by the polarity of the magnetic field which permeates the tube, at least one output electrode of each beam position is directly coupled to the spade of the adjoining beam position which lies in the direction opposite to the direction in which the magnetic field tends to influence the advancement of the beam, and a source of modulation energy coupled to said lastmentioned spade and across its load impedance.

7. A modulation system in accordance with claim 6, wherein the direct coupling between the output electrodes and spade electrodes is done inside the tube envelope.

8. A magnetron beam tube comprising, within an evacuated envelope, an electron emitting cathode, an elongated electrode partially surrounding said cathode, said elongated electrode having an arcuate cross-sectional configuration, a plurality of trough-shaped beam-forming and beam-holding spade electrodes disposed between the open edges of said elongated electrode, said spade electrodes being spaced from each other and from said elongated electrode to form at least a pair of adjoining spades, and electron receiving target electrodes, one of said target electrodes being disposed opposite the space between each pair of adjoining spades, and another target electrode being disposed opposite the space between the elongated electrode and the spade adjacent thereto, and a grid structure disposed adjacent to at least one target electrode on the side thereof which faces generally towards said cathode.

9. A magnetron beam tube comprising, within an evacuated envelope, an electron emitting cathode, an elongated electrode partially surrounding said cathode, said elongated electrode having an arcuate cross-sectional configuration which exceeds a semi-circle, a pair of troughshaped beam-forming and beam-holding spade electrodes disposed between the open edges of said elongated electrode, said spade electrodes being spaced from each other and from said elongated electrode, and electron receiving target electrodes, one of said target electrodes being disposed opposite the space between said pair of spades and opposite the space between the elongated electrode and one of the spades adjacent thereto, and a grid structure disposed adjacent to at least one target electrode on the side thereof which faces generally towards said cathode.

10. A magnetron beam tube comprising, within an evacuated envelope, an electron emitting cathode, an elongated electrode partially surrounding said cathode, said elongated electrode having an arcuate cross-sectional configuration, a plurality of trough-shaped beam-forming and beam-holding spade electrodes disposed between the open edges of said elongated electrode, said spade electrodes being spaced from each other and from said elongated electrode, and electron receiving target electrodes, each of said target electrodes being of L shaped cross-sectional configuration, one of said target electrodes being interleaved between the open portion of each spade, and a grid structure disposed adjacent to at least one target electrode on the side thereof which faces generally towards said cathode.

11. A magnetron beam tube in accordance with claim 10, wherein the target electrodes having a grid structure disposed adjacent thereto have a secondary electron emission ratio which is greater than unity.

12. A magnetron type beam tube comprising, within an evacuated envelope, an elongated electron emitting cathode, an elongated electrode of arcuate cross-sectional configuration, said elongated electrode partially surrounding said cathode, and electrode groups providing two beam paths, each beam path including a beam-forming and beam-holding spadeelectrode, said spade electrodes being disposed side by side in the space between the edge portions of said elongated electrode which extend in the direction of elongation thereof, and an electron receiving target electrode mounted in each beam path, the target electrode of each beam position being disposed adjacent to the spade electrode thereof and having a surface which faces generally towards said cathode, impedance means conductively connected between one spade electrode and said cathode, the target electrode of the beam path including said last-mentioned spade being directly coupled to the spade of the other beam position, and terminal means connected to the spade having said impedance means connected thereto whereby a modulating signal may be up plied across said impedance means.

13. A magnetron type beam tube in accordance with claim 12, wherein a magnetic field source having flux lines permeating said tube is provided, said flux lines tending to influence the electron beam of said tube to advance in a direction determined by the polarity of the field, and the spade which is coupled to the target electrode is disposed, with respect to the target electrode to which it is coupled, in the direction the magnetic field. tends to infiuence the beam.

14. A magnetron type beam tube comprising, within an evacuated envelope, an elongated electron emitting cathode, an elongated electrode of arcuate cross-sectional configuration, said elongated electrode partially surrounding said cathode, and a plurality of beam-receiving electrode groups, each electrode group including a beamforming and beam-holding spade electrode, said spade electrodes being disposed side by side in the space between the edge portions of said elongated electrode which extend in the direction of elongation thereof, and an electron receiving target electrode, the target electrode of each electrode group being disposed adjacent to the spade I electrode thereof and having a surface which faces generally towards said cathode, impedance means conductively connected between one spade electrode and said cathode, the target electrode of the group including said last-mentioned spadebeing directly coupled to the spade of an adjoining group, and terminal means connected to the spade having the impedance means connected thereto whereby a modulating signal may be applied across said impedance means.

15. A magnetron type beam tube in accordance with claim 14, wherein a grid member is disposed adjacent to a surface of at least one target electrode.

16. A magnetron type beam tube comprising, within an evacuated envelope, an elongated electron emitting cathode, an elongated electrode of arcuate cross-sectional configuration, said elongated electrode partially surrounding said cathode, and a plurality of electrode groups, each group including a beam-forming and beam-holding spade electrode and providing a beam position of the tube, said spade electnodes being disposed side by side in the space between the edge portions of said elongated electrode which extend in the direction of elongation thereof, and an election relieving target electrode, the target electrode of each beam position being disposed adjacent to the spade electrode thereof and having a surface which faces generally towards said cathode, at least one of said target electrodes having a secondary electron emission ratio which is greater than unit, a resistor conductively connected between one spade electrode and said cathode, the target electrode of beam position including said last-mentioned spade being directly coupled to the spade of an adjoining beam position, and terminal means connected to the spade having the impedance means connected thereto whereby a modulating signal may be applied across said impedance means.

17. A magnetron type beam tube in accordance with claim 16, wherein a secondary electron collector electrode is disposed adjacent to each target electrode having a secondary electron emission ratio which is greater than unity, said collector electrode being so disposed with respect to other electrodes that substantially all secondary electnons emitted from the target electrode are col looted by the collector electrode.

18. A modulation system including an electron beam tube having a cathode, a plurality of target electrodes spaced from said cathode and adapted to receive an electron beam therefrom, and a spade electrode associated 'With each target electrode and adapted to form and hold an electron beam on its associated target electrode; means coupled to said tube for determining the movement of an electron beam in a predetermined direction; means coupled to at least one spade electrode for setting its potential at about cathode potential; and means coupled to said one spade electrode for applying a modulating signal thereto.

19.A modulation system including an electron beam tube having a cathode, a plurality of target electrodes spaced from said cathode and adapted to receive an electron beam therefrom, and a spade electrode associated with each target electrode and adapted to form: and hold and electron beam on its associated target electrode; means coupled to said tube for switching an electron beam in a predetermined direction; each target being electrically connected to the preceding spade electrode so that current flow to any target electrode lowers the potential of the spade to which it is connected; and means coupled to said spade electrodes for applying a modulating signal [thereto.

2 0. A modulation system including an electron beam tube having a cathode, a target electrode spaced from said cathode and adapted to receive an electron beam and produce an output signal therefrom, a first spade electrode associated with said target electrode and. adapted to form and hold an electron beam on said associated target electrode, the space between said cathode and said target defining a current flow path, an electrode outside of said current flow path for modulating the current flow in said current flow path, and means providing a longitudinal magnetic field in said tube, said magnetic field and electric fields within said tube co-acting to control the flow of an electron beam therein and causing said beam to tend to move in a characteristic direction known as the leading direction, said last-mentioned electrode being oriented on the side of said electron beam and said current flow path representing the lagging direction of the beam so that the tendency of the beam is to move away from said electrode.

21. A modulation system including an electron beam tube having a cathode, a target electrode spaced from said cathode and adapted to receive an electron beam and produce an output signal therefrom, a first spade electrode associated with said target electrode and adapted to form and hold an electron beam on said associated target electrode, the space between said cathode and said target defining a current flow path, and a modulating electrode 12 outside of said current flow path and lagging said target electrode for modulating the current flow in said current flow path.

22. The system defined in claim 21 and including an auxiliary electrode defining a portion of a cylinder and having one edge adjacent to said target electrode and one edge adjacent to said modulating electrode.'

23. A modulation system including a magnetron beam tube having a cathode, a target electrode spaced from said cathode and adapted to receive an electron beam and produce an output signal therefrom, and a first spade electrode associated with said target electrode and adapted to form and hold an electron beam on said target electrode, magnetic means coupled to said tube providing an axial magnetic field therein, the combination of the electric fields in said tube and said magnetic field determining the movement'of an electron beam in a predetermined direction, a second spade electrode positioned adjacent to and lagging said first spade, means coupled to said second spade electrode for setting its potential at about cathode potential, and means coupled to said second spade electrode for applying a modulating signal thereto for modulating the current flow to said target electrode.

2.4; The system defined in claim 23 wherein said tube includes an auxiliary electrode leading said target electrode and biased to prevent the switching of an electron beam thereto from said target electrode.

25. The system defined in claim 23 wherein said tube includes an auxiliary electrode in the form of a portion of a cylinder enclosing said cathode and having one edge adjacent to and leading said target electrode and one edge adjacent to said second spade electrode, said auxiliary electrode assisting in defining the current flow path between said cathode and said target electrode and being biased to prevent the switching of an electron beam thereto from said target electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,416,298 =Fisk Feb. 25, 1947 2,495,738 Labin et al Jan. 31, 1950 2,569,971 Ballantyne Oct. 2, 1951' 2,576,093 Arditi Nov. 27, 1951 2,797,357 Kuchinsy et al June 25, 1957 2,802,103 Fitzpatrick et a1 Aug. '6, 1957 2,839,702 Sin-Pih Fan et al June 17, 1958 

20. A MODULATION SYSTEM INCLUDING AN ELECTRON BEAM TUBE HAVING A CATHODE, A TARGET ELECTRODE SPACED FROM SAID CATHODE AND ADAPTED TO RECEIVE AN ELECTRON BEAM AND PRODUCE AN OUTPUT SIGNAL THEREFROM, A FIRST SPADE ELECTRODE ASSOCIATED WITH SAID TARGET ELECTRODE AND ADAPTED TO FORM AND HOLD AN ELECTRON BEAM ON SAID ASSOCIATED TARGET ELECTRODE, THE SPACE BETWEEN SAID CATHODE AND SAID TARGET DEFINING A CURRENT FLOW PATH, AN ELECTRODE OUTSIDE OF SAID CURRENT FLOW PATH FOR MODULATING THE CURRENT FLOW IN SAID CURRENT FLOW PATH, AND MEANS PROVIDING A LONGI- 